Recently, due to the quick growth of smart phone penetration, data traffic on mobile network is experiencing significant growth. At the same time, more affordable service and application are expected by end users. Therefore, many operators are facing the challenge to offload their overloaded networks and reduce the transport and peering cost. Facing this situation, so-called Content Distribution Networks have been proposed attracting more and more attention. When introducing Content Distribution Network or Content Delivery Network—CDN—system into mobile networks, also being referred to as mobile CDN, there are many potential issues. One important issue is how to select an appropriate CDN server to serve a moving mobile terminal or user equipment—UE—by considering mobile network specific characteristics, such as UE movement.
First of all, in contrast to CDN being realized in fixed networks where the IP address is usually used as location information, in mobile networks, the same IP address is allocated to a UE when roaming under the same P-GW/GGSN, e.g. all UEs under the same P-GW/GGSN get allocated an IP address from the same sub-network. Hence, for mobile UEs, the IP address might not be sufficiently effective to be used as location information to find an appropriate CDN server, also being referred to as CDN distribution or delivery node—CDN DN—, e.g. when some CDN DNs are deployed below Gi (UMTS)/SGi (EPS) interface (in other words, inside of mobile networks). The CDN DN stores copies of the content and delivers content to the client according to instructions from the control logic in a CDN control node, —CDN CN—. The CDN CN generally decides about how to react to a content request, what content is to be delivered and from which CDN DN the content shall be delivered. This node might further control in which CDN DN copies of certain content is stored.
A further issue might to be considered when selecting a CDN DN to serve a moving UE: the closer a CDN DN is to the UE, the better with respect to transport bandwidth saving and latency reduction. On the other hand, there is an increasing risk of CDN DN relocation and service interruption for the moving UE.
In case an CDN server below Gi/SGi is selected, the existing mobility management mechanism of 3GPP networks may not be appropriate to ensure the service continuation for moving terminals like that of SIPTO/LIPA situation.
An introduction of CDN into mobile networks might mean that some CDN DNs are deployed in mobile networks, i.e. below Gi/SGi interface, and some other CDN DNs are deployed above Gi/SGi interface. Generally, above Gi/SGi refers to a CDN DN being deployed outside of the mobile network and below Gi/SGi refers to a CDN DN within or comprised by the mobile network. In case of a CDN DN below Gi/SGi, this CDN DN can be deployed in the radio access network (RAN) or the core network (CN). One issue thereof might be related to security and charging, e.g. the CDN CN selecting an appropriate edge node to serve a specific moving UE. For example, due to security requirements, for a UE, certain media content might not be allowed to be provided by an CDN server below SGi/Gi interface although the gains may be bigger from performance point of view. In addition, due to requirement of lawful interception or charging, for some UEs, a CDN DN located in CN instead of a CDN DN located in RAN is preferred to be used to serve the mobile UE.
One important issue of CDN system is the CDN delivery node (DN) or service node selection. Currently, several typical approaches are proposed such as DNS based, HTTP redirection or URL rewriting. A recent proposal/realization of a server selection proposes a GSLB (global service load balancer function) of a CDN provider selecting the best service node for a UE based on IP address of a local DNS server which is usually associated with the UE IP address, and, and other information such as resource status of service node, link status from UE to service node, etc. The SLB locally selects the specific cache node to serve the UE by various mechanisms such as HTTP redirection, URL rewriting. In other words, the central control system (CDN CN) selects an edge server by GSLB at macro level. The SLB located in the CDN Edge server/node will select locally which Cache will be used to the UE at micro level.
Several local caches may be transparent to out side of the CDN edge server from IP level. Several Caches may share the same public IP address to outside UEs such that only the CDN Edge server/node knows the internal topology of local Cache nodes controlled by it.
However, the above-described mechanism has been developed with a focus to fixed networks rather than to mobile network requirements. In contrast to CDN on fixed networks where IP address can be used as location information, in mobile networks, the same IP address is allocated to a UE when moving under the same P-GW/GGSN, e.g. each UE served by the same P-GW/GGSN is a allocated a IP address. In this situation, the IP address isn't effective to be used as location information to find an appropriate CDN DN node (e.g. the node to serve a UE locally with cached content) when some CDN DN nodes are deployed below Gi/SGi interface. Further, compared with fixed CDN system, the mobility of UE might be an issue to be considered when selecting a CDN DN to serve a moving UE: The closer a CDN DN is to a UE, the more gains are possible with respect to transport bandwidth saving and latency reduction; on the other hand there is an increased risk of a CDN DN relocation and service interruption for the moving UE.